1. Field of the Invention
The present invention relates to a method for dimerizing an olefin such as ethylene, propylene, butene, pentene, decene or tetradecene by means of a certain specific catalyst.
The dimerization product of an olefin produced by the dimerization method of the present invention may be hydroformylated, for example, by reacting it with carbon monoxide and hydrogen in the presence of e.g. a Group VIII metal catalyst such as a Rh catalyst, and the obtained aldehyde may further be hydrogenated to obtain an alcohol. Such an alcohol may be esterified with a carboxylic acid such as phthalic acid to obtain an industrially useful compound which can be used as a plasticizer for synthetic resins.
2. Discussion of Background
Many studies have been made with respect to a catalyst system by which a monoolefin such as ethylene, propylene, butene, pentene, decene or tetradecene is uniformly dimerized. As the catalyst system, a Ziegler type catalyst employing a transition metal as a principal catalyst component, is usually superior from the viewpoint of the selectivity for a dimer of a monoolefin. Especially when a catalyst obtained from a mixture of a nickel compound and an organic aluminum halide, is used, excellent results have been obtained with respect to both the dimerization activity and the selectivity.
Further, many studies have also been made with respect to a catalyst system wherein an organic phosphorus compound is used as a third catalyst component together with the above-mentioned catalyst components, and it is known that such a catalyst component is influential over the catalytic activity and the product selectivity. As catalyst systems wherein such organic phosphorus compounds are incorporated, 1 Japanese Examined Patent Publication No. 34007/1971 discloses a catalyst system comprising a .pi.-allyl type nickel complex, an organic aluminum halide and an organic phosphine, 2 Japanese Examined Patent Publications No. 30241/1973 and 30041/1975 disclose catalyst systems comprising organic phosphine complexes of nickel represented by (R.sub.4 P).sup.+ (R.sub.3 PNiX.sub.3).sup.- (wherein R is a hydrocarbyl group or hydrogen, and X is chlorine, bromine or iodine) and NiX'.sub.2 (PR'.sub.3).sub.2 (wherein X' is chlorine, bromine or iodine, and R' is an alkyl group), respectively, and 3 Japanese Unexamined Patent Publication No. 339174/1993 discloses a catalyst system wherein a halogenated phenol, water and a sulfonic acid are added as additives to a nickel compound, an alkylaluminum and a trivalent phosphorus compound, wherein the trivalent phosphorus compound may be not only the above-mentioned organic phosphine but also a trivalent organic phosphite compound such as triethyl phosphite, tri-t-butyl phosphite, triphenyl phosphite or tri-p-tolyl phosphite.
As described above, various organic phosphorus compounds have been proposed as catalyst components to be used for the dimerization reaction, but these compounds are not necessarily satisfactory for industrial operation. Namely, the catalyst system of the above 1 is extremely unstable against air, hence its handling is troublesome, and it also has a drawback that synthesis of the catalyst is complex. Also, the catalyst systems of the above 2 involve a difficulty for industrial operation, since it is required to separately prepare complicated nickel complexes. The catalyst system of the above 3 exhibits a high catalytic activity for dimerization of a lower .alpha.-olefin such as ethylene or propylene, but its dimerization activity is inadequate for an internal olefin, for example, a substrate such as 2-butene. Therefore, it is not satisfactory in the catalytic efficiency for a starting material substrate containing an internal olefin.
Thus, catalyst systems wherein various organic phosphorus compounds are used as co-catalysts, have been proposed as catalysts for dimerization reactions of olefins, but they are not necessarily satisfactory for industrial operation from the viewpoint of the stability of catalysts, the preparation method, the catalytic efficiency or the product selectivity and thus still have problems to be solved.